The visual system of the brain produces a perception of three-dimensionality by combining the two slightly different images coming from the eyes. An image displayed on a two-dimensional display screen can give rise to the same perception without the need of special viewing glasses or the like, if the display screen is autostereoscopic, i.e. in itself capable of emitting slightly different information to the right and left eye of the viewer. The two autostereoscopic display technologies that are most widely used for this purpose at the time of writing this specification are known as the parallax barrier principle and the lenticular principle, although also other approaches are known as well.
FIG. 1 is a simple schematic example of a known parallax barrier type liquid crystal display. A liquid crystal layer 101 comprises right-eye subpixels and left-eye subpixels marked with R and L respectively. A backlighting layer 102 emits light from behind the liquid crystal display. A parallax barrier layer 103 contains slits that only allow light to propagate through the right-eye subpixels to the right eye of the viewer and through the left-eye subpixels to the left eye of the viewer. It is also possible to have the parallax barrier layer 103 in front of the liquid crystal layer 101 instead of between it and the backlighting layer 102.
FIG. 2 is a simple schematic example of a known lenticular type liquid crystal display. Also here the liquid crystal layer 201 comprises right-eye subpixels and left-eye subpixels. The backlighting layer 202 emits light through the liquid crystal layer 201. A layer 203 of lenticulars, i.e. cylindrical lenses, collimates the light so that light rays coming through a right-eye subpixel continue parallelly towards the right eye of the viewer and light rays coming through a left-eye subpixel continue parallelly towards the left eye of the viewer.
FIG. 3 illustrates schematically a known principle for generating three-dimensional image information of a group of imaged objects. Two horizontally separated cameras 301 and 302 take pictures at the same time but otherwise independently of each other, resulting in two so-called raw images 303 and 304 respectively. Images of the objects appear at different locations in the raw images, because the cameras 301 and 302 see the imaged objects from different directions. It should be noted, though, that the differences in the raw images appear in highly exaggerated proportion in FIG. 3 compared to most practical solutions, because for reasons of making FIG. 3 graphically clear the imaged objects are drawn very close to the camera arrangement. Together the raw images 303 and 304 constitute a stereograph that could be displayed using any suitable display technology, including but not being limited to those illustrated in FIGS. 1 and 2.
There are no widespread standards that would define the parameters that affect the generation of stereographs or their presentation on display screens. Numerous parameters have a significant effect, such as the separation between cameras; focal length; size, resolution and angular pixel pitch of the CCD (Charge-Coupled Device) arrays in the cameras; size, resolution and pixel structure of the display; default viewing distance; and the amount of scaling, cropping and other processing that is required to map the raw images to the subpixel arrays, time-interlaced fields or other display elements that eventually present the fused image to the viewer. The lack of standards means that a stereographic image taken with a certain imaging arrangement and prepared for presentation on a particular display type is not likely to work well on any other display type.
The incompatibility problem will become more and more important when three-dimensional imaging and autostereoscopic displays find their way to simple and inexpensive consumer appliances, such as portable communication devices, where conventional cameras and high-quality two-dimensional displays are already in widespread use. A user that has taken a three-dimensional image with a portable communication device of one brand wants to be sure that he can transmit the image to another user, who can view it correctly irrespective of which brand of a device the recipient has.
A US patent publication number US 2004/0218269 A1 discloses a 3D Data Formatter, which acts as a format converter between various known interlacing techniques and is also capable of certain basic picture processing operations, such as zooming, cropping and keystone correcting. Simply changing between presentation formats does not solve the problem of inherent incompatibility between displays that may be of different size and may have a different default viewing distance. A weakness of the reference publication is also that the solution considered therein can only work between formats and interlacing techniques that the formatter device knows in advance. The reference publication does not consider any way of generating good fusible 3D image content for any receiving device, the features of which are not yet known.